In the field of biology and medicine, “microdissection” refers to a method with which a small piece can be cut out from a generally flat sample or biological specimen (for example, cells, a cell agglomeration, or a tissue section) using a narrow, focused laser beam. The cut-out piece is, as a rule, physically separated from the biological specimen and is thus available for further biological or medical (e.g. histological) investigations. The manner in which the sample is prepared depends, inter alia, on the laser microdissection method with which processing of the sample is to be performed.
DE 102 34 755 A1, which is hereby incorporated by reference herein, describes a carrier apparatus for a biological sample or specimen that is cuttable by means of laser microdissection. This carrier apparatus is a Petri dish in which, however, the base is embodied in the form of a self-supporting laser-light-absorbing film, the sample or specimen being arranged on the film. The laser microdissection device provided therein encompasses a transmitted-light microscope having an X-Y stage on which the carrier apparatus with the specimen is arranged. Arranged below the specimen is a collection receptacle for collecting the cut-out sample region.
A laser beam proceeds from a UV laser and is coupled into an incident illumination beam path. The laser beam proceeds via an optical system to an objective that focuses the laser beam onto the sample. The laser beam is movable relative to a biological specimen or to the film. Also, for example, a laser scanning device is arranged in the illumination beam path, with which device the laser beam is deflected. Alternatively, the microscope stage is moved relative to the laser beam.
A method of this kind has already been described in the article “Cell surgery by laser microdissection: a preparative method,” G. Isenberg, W. Bielser, W. Meier-Ruge, E. Remy, Journal of Microscopy, Vol. 107, May 1976, pp. 19-24. Here a focused laser beam of a pulsed UV laser is directed from above onto a (preferably biological) sample, and the focused laser beam is moved around a sample region of interest along a continuous cut line. The sample region of interest is thereby completely detached from its surroundings and falls into a collection apparatus. In DE 102 34 755 A1, a collection apparatus, into which the cut-out specimen portion along with a piece of film falls, is arranged below the carrier apparatus.
A more recent method and an apparatus for laser microdissection are described by DE 100 43 506 C1. Here a focused laser beam is directed from above onto a (preferably biological) sample. In a first step, the focused laser beam is moved around a sample region of interest along an open cut line that largely encloses the sample region of interest; there remains, between the beginning and end of the cut line, a stable web that continues to connect the sample region of interest to the surrounding specimen. In a second step, the web is cut through with a single focused laser pulse directed onto the web, the cut width having previously been adapted to the width of the web, i.e. enlarged. The sample region of interest is completely detached from its surroundings by the last cutting laser pulse, and falls downward. As compared with the method recited previously, this method has the advantage that toward the end of the cutting operation it prevents the almost-cut-out sample region from swinging away or rotating.
WO 2006/024392 A2, which is hereby incorporated by reference herein, describes a carrier apparatus for laser microdissection that is usable in an inverted microscope. Here the biological specimen is located on a (generally conventional) specimen slide, and the laser beam used for laser microdissection is focused from below, i.e. through the specimen slide, onto the biological specimen, and the region of interest is correspondingly cut out. For separation of the selected specimen region, the latter is then catapulted away from the specimen slide, with the aid of an additional laser pulse, to a collection apparatus arranged above the specimen slide and arranged movably in its position relative to the specimen slide. This separation procedure is also referred to as a laser catapulting method.